Magnetically operated proximity switch



March 121968 E. H. IRASEK MAGNETICALLY OPERATED PROXIMITY SWITCH Filed July 7,- 1966 z 5 WWW V 7 mum/ M MW 0.

United States Patent Oflice 3,373,387 Patented Mar. 12, 1968 3,373,387 MAGNETICALLY OPERATED PROXIMITY SWITCH Eugene H. .lrasek, Inglewood, Califl, assignor to Houston Fearless Corporation, Los Angeles, Calif., a corporation of California Filed July 7, 1966, Ser. No. 563,465 7 Claims. (Cl. 335-207) ABSTRACT OF THE DISCLOSURE A magnetically operated proximity switch employing a pair of permanent magnet blocks having magnetic pole faces at their front and back surfaces and magnetized therebetween, with the blocks spaced apart in a direction at right angles to their direction of magnetization. A magnetic reed switch is located adjacent the side faces of the magnet blocks other than the magnetic pole faces thereof with the longitudinal axes of the reeds extending generally in the direction of the spacing between the blocks and with the reeds normally separated. Thes polarities of the front and back faces of the magnet blocks are reversed so that the flux passing through the reeds between the back pole faces is opposite in direction to the flux passing through the reeds between the front pole faces to affect cancellation of the fluxes to an extent that the resultant flux is insufficient to close the reeds in the absence of an element of magnetic material adjacent the front magnetic pole faces to bleed off the flux thereat. To increase the sensitivity of the proximity switch the magnetic reeds are offset from the center plane of the permanent magnet blocks away from their front faces to establish a normally predominant resultant flux through the reeds between the back pole faces. The spacing between the permanent magnets is made sufficiently small to substantially restrict the depth of the fringing field from the pole faces so that the proximity switch will be responsive to the proximity of a magnetic element regardless of the presence of a magnetic background at a greater distance.

The present invention relates generally to a magnetic sensor or pickup for detecting the presence of a magnetic element adjacent to the sensor. The magnetically operated proximity switch according to the present invention employs a magnetic reed switch which may be of normally closed, normally open or double-throw character and which is operated from its normal position by the proximity of an. element of magnetic material adjacent the sensor.

Magnetic reed proximity switches known in the prior art, of which examples are shown in the patents to Hess No. 3,187,127 and Deshautreaux, Jr. No. 3,205,323 have inherent disadvantages of which complexity and lack of sensitivity are two of the more important. Such magnetic reed proximity switches are not only insensitive to the presence of the edge of a thin magnetic sheet, but, even more important, they fail to discriminate the proximity of such a magnetic element against a relatively close magnetic background.

The magnetic sensor of the switch of the present invention is reliably sensitive to the proximity of a single, edgewise, relatively thin ferrous sheet while at the same time the sensor is quite discriminative so that a background of magnetic material a relatively short distance from the sensor will not daversely effect its response to a closer single element as above described.

By way of example, in one physical embodiment of the invention the magnetic sensor recognized the proximity of a relatively thin magnetic element at a distance of g of an inch while failing to respond to a background of magnetic material only A" from the sensor. This magnetic sensor so responded to proximity of the magnetic element with the magnetic background present at the same time and at the distances specified.

The proximity switch of the present invention employs a pair of permanent magnet blocks spaced apart generally at right angles to the relative direction of passage of the magnetic element to be sensed. A magnetic reed switch constituting the active member of the sensor is located with respect to the permanent magnets so that oppositely directed magnetic fluxes therefrom normally cancel sufficiently to prevent actuation of the switch. One of the magnetic fluxes is bled off by proximity of a magnetic element to be sensed whereupon the dominating flux will effect operation of the magnetic reed switch.

The magnetic reed switch may be offset from the central plane of the permanent magnets away from the magnetic element to be sensed to increase the sensitivity of the switch. The spacing between the permanent magnet blocks will determine the depth of the fringing magnetic field in the proximity sensing face of the sensor and there fore will effect the discrimination of the sensor against a magnetic background. The amount of the offset of the reed switch, the amount of spacing between the magnets, and the strength of the magnets may be individually controlled in the design of a sensor to change the response characteristics thereof.

It is therefore a primary object of the present invention to provide a magnetic reed proximity switch of increased sensitivity.

Another primary object of this invention is the provision of a magnetic reed proximity switch with improved discrimination against a magnetic background.

Another object of this invention is the provision of a magnetically operated proximity switch of simple and inexpensive construction without sacrifice of sensitivity and discrimination.

Other objects and features of the invention will be apparent to those skilled in the art from the following specification and the appended drawings in which:

FIGURE 1 is a perspective view of a magnetic reed proximity switch according to the present invention with a magnetic element to be sensed located in proximity thereto;

FIGURE 2 is a vertical sectional view through the proximity switch of the present invention taken on the offset line 2-2 of FIGURE 1;

FIGURE 3 is a horizontal sectional view through the proximity switch of this invention on the line 3-3 of FIGURE 1;

FIGURE 4 is a diagrammatic and perspective view of the switch of the present invention showing the field disposition with respect to the magnetic reeds of the switch which may be connected as normally closed, or normally open, or double-throw normally closed, normally open; and

FIGURE 5 is a bottom view of FIGURE 4 taken in the direction of the arrow 5 in FIGURE 4.

Referring first to FIGURES 1-3, the embodiment 10 illustrated therein comprises a pair of permanent magnet blocks 11 and 12, for example of barium ferrite or other permanent magnet material. The magnets 11 and 12 are mounted within recesses 13 and 14 in a block 15 of nonmagnetic material such as aluminum, plastic or the like. The magnetic blocks 11, 12 may be cemented orfrictionally or mechanically interlocked in the recesses 13 and 14 and the recesses may be closed at the front by a plate 16 cemented or otherwise fixed to the block 15 and of a like non-magnetic material.

The permanent magnet blocks 11 and 12 may be disposed in various relations and are illustrated in the drawing as super-imposed vertically, with their pole faces at the front and back and magnetized in a horizontal transverse direction. The permanent magnets 11 and 12 are mounted in reverse polarity so that the North face of one magnet is above the South face of the other magnet and vice versa. The permanent magnets 11 and 12 are spaced apart a vertical distance y, as shown in FIGURE 2, which determines the effective depth of the fringe magnetic field indicated by the broken lines 17.

At one side of the permanent magnets 11 and 12 an opening 18 extends vertically through the block and a magnetic reed switch 19 is cemented or frictionally engaged therein. The magnetic reed switch 19 is of the normally open type with magnetic reeds 21 and 22 mounted within a sealed and evacuated non-magnetic and nonconducting container 23 of, for example, glass or like material. The magnetic reeds 21 and 22 are connected to exterior electrical terminals 24 and 25, respectively.

As shown in FIGURE 3, the longitudinal axis of the reed switch 19 is offset fro-m the center vertical plane of the permanent magnets by a distance x to increase the sensitivity of the sensor. By this offset the flux threading the magnetic reeds 21, 22 between the back pole faces of the magnets is greater than the flux through the magnetic reeds from the front pole faces. That is, the flux flowing from the North pole of the lower permanent magnet through the magnetic reeds to the South pole of the upper permanent magnet will, in the absence of the magnetic element 26 to be sensed, be stronger than the magnetic flux in the reverse direction through the magnetic reeds from the North pole of the upper permanent magnet to the South pole of the lower permanent magnet, in the manner illustrated in FIGURE 4. Therefore the magnetic fluxes will not entirely cancel and there will remain a resultant flux from the predominance of the flux from the back pole faces. This resultant flux is not however sufficiently strong to operate the reed switch nor to hold the reeds in engagement in the absence of a magnetic element 26.

The magnetic element to be sensed may take any form, such as a thin sheet edge, the element 26 in the embodiment illustrated being a thin U-shaped piece of ferrous tmetal clipped on the forward edge of a non-magnetic card 27 which has been pulled forwardly from a body of like cards and magnetic clips indicated generally by the numeral 28. The clips of ferrous magnetic material in the general stack of group of FIGURE 3 form a magnetic background against which the switch of this invention discriminates so that it is not affected by the presence of such a magnetic mass at a distance, by way of example, of as little as while at the same time being operated by the single magnetic element shown adjacent the sensor in FIGURE 3 and positioned at a distance, for example, of The switch responds accurately and reliably to the proximity of the single projected magnetic element even with the large magnetic background present at the same time. As illustrated in FIGURE 3 the body of cards 28 is moving in the direction of the arrow 29 and this invention will detect, and indicate by the closing of the reed switch 19, the movement of the projected element 26 into proximity with the near edge thereof.

As the magnetic element 26 approaches the near edges of the permanent magnets 11 and 12, that is, the edges of the North face of the upper magnet and the South face of the lowe magnet, the field between these faces which passed through the magnetic reeds of the switch 19 and which is indicated by the dotted line 31 of FIGURE 4 is greatly decreased because it is bled off through the low reluctance path through the magnetic element 26 at the front of the sensor. With the field 31 thus weakened, the fields 32 passing through the magnetic reeds of the switch between the back pole faces of the permanent magnets,

4 that is, the North face of the lower magnet and the South face of the upper magnet predominates and the resultant flux passing through the reeds of the switch becomes sufficiently strong to attract the reeds into closed position.

When the reed switch 19 closes it has performed its function of indicating the proximity of the magnetic element 26. As the element 26 passes across the front face of the sensor 10, the resultant flux may decrease somewhat but still maintains the reeds closed until the element 26 passes the permanent magnets, whereupon the resultant flux returns to its inactive value and the reeds open to place the proximity switch in normal position ready to signal the approach of another magnetic element 26 extended toward the sensor thereof from the main body of elements 28.

FIGURES 4 and 5 illustrate the operation of a sensor with a magnetic reed switch employing two magnetic reeds 21A and 22A and a conducting non-magnetic reed 33. It will be understood that FIGURE 4 is diagrammatic and that the reeds 21A, 22A and 33 will be disposed within a capsule enclosure such as 23 of FIGURE 2 and will have appropriate terminals. The operation of the reed switch of FIGURES 4 and 5 is as previously described to engage the reeds 21A and 22A upon the approach of a magnetic element 26A which will bleed off the field 31 and permit the field 32 to predominate to draw the magnetic reeds together.

The switching operation of the reed switch of FIGURE 4 will depend upon the electrical connections thereto. The reeds 22A and 33 form a normally closed circuit whereas the reeds 21A and 22A form a normally open circuit. If only a normally closed switch is desired to operate to open position, then only the reeds 22A and 33 have their terminals connected in circuit. If only a normally open switch is desired, as in FIGURE 2, then only the reeds 21A and 22A have their terminals in circuit. If a double-throw, normally closed, normally open switch is desired then the terminals of the reeds 21A, 22A and 33 are connected in circuit, the terminals of 22A and 33 forming a closed circuit to be opened on actuation of the switch while the reeds 21A and 22A form a normally open circuit to be closed upon actuation of the switch.

It will be understood that the amount of the offset x Will determine the relative predominance of the flux 32 over the flux 31 and the sensitivity of the switch. It will be obvious that the resultant flux must never be sufiicient to hold the reeds 21 and 22 together in the absence of a magnetic element 26. The spacing between the permanent magnets represented by the distance y in FIGURE 2 will determine the depth of the fringe field and the discrimination of the sensor in selecting a magnetic element 26 from the bacground magnetic mass passing therewith across the sensor but at a greater distance. Variations in the offset x and the spacing y, as well as in the strength of the magnets provide close control of the response characteristics of the sensor, its sensitivity and discrimination.

It is therefore seen that the magnetic reed proximity switch of the present invention is responsive to the proximity of a relatively thin, low-mass magnetic element, that it differentiates between such an element and a nearby magnetic background, and at the same time provides for reliable restoration of the reed switch to its initial condition after departure of the element being sensed. While certain preferred embodiments of the invention have been illustrated and described herein it will be understood that the invention is not limited thereto as many variations will be apparent to those skilled in the art and the invention is to be given its broadest interpretation within the terms of the following claims.

I claim:

1. A proximity switch comprising: a pair of permanent magnet blocks having magnetic pole faces at their front and back surfaces and being magnetized therebetwecn, said blocks being spaced apart in a direction at right angles to their direction of magnetization; a mangetic reed switch located adjacent the side faces of said blocks other than the magnetic pole faces with the longitudinal axes of the reeds extending generally in the direction of the spacing between the blocks, the reeds being normally separated, the polarity of the front and back pole faces of said blocks being reversed so that the flux passing through the reeds between said back pole faces is opposite in direction to the flux passing through the reeds between said front pole faces whereby the fluxes will cancel to an extent that the resultant flux is insufficient to close the reeds, the proximity switch detecting the passage of a magnetic element across the front faces of said blocks by bleeding off flux between the pole faces thereat whereby the flux through the reeds between the back pole faces predominates to increase the resultant flux and cause the magnetic reeds to engage.

2. The proximity switch defined in claim 1 in which the front, back and side faces of said blocks lie in substantially common planes.

3. The proximity switch defined in claim 1 in which the resultant flux is insufiicient to hold the reeds in engagement in the absence of a magnetic element at the front faces of the blocks.

4. The proximity switch defined in claim 1 in which said magnetic reeds are offset from the center plane of the permanent magnets away from their front faces whereby to establish a normally predominant flux through the reeds between the back pole faces to increase the sensitivity of the switch.

5. The proximity switch defined in claim 1 in which the spacing between said permanent magnets is sufliciently small to substantially restrict the depth of the fringing field from the pole faces whereby the switch will discrimimate in indicating the proximity of a magnetic element regardless of the presence of a magnetic background at a greater distance therefrom.

6. The proximity switch defined in claim 1 including a non-magnetic conducting reed normally contacting one of the normally separated magnetic reeds to establish a normally closed circuit which is opened when said contacted magnetic reed moves into engagement with the other magnetic reed.

7. The proximity switch defined in claim 1 in which said permanent magnet blocks are substantially identical, have their pole faces facing in the same directions but with opposite polarity, and have their side edges substantially in alignment.

References Cited UNITED STATES PATENTS 3,205,323 9/1965 Deshautreaux 335-207 FOREIGN PATENTS 1,033,762 7/ 1958 Germany.

BERNARD A. GHJHEANY, Primary Examiner. R. ENVALL, Assistant Examiner. 

